The present invention relates to long blades for a high and low pressure sides-integrated steam turbine, using a noble heat resistant alloy, a high and low pressure integral steam turbine using the long blades, and a combined cycle power generation system.
At present, 12Cr--Mo--V--N steel is used for steam turbine blades. In recent years, it has been desired to raise the thermal efficiency of a fossil fuel power plant in view of energy-saving, and make apparatuses used therefore compact in view of space-saving.
Elongation of the turbine blades is an effective means for improving the thermal efficiency and making the apparatuses compact. Therefore, the length of blades of the final stage tends to be increased year by year. Thereby, under conditions in which the steam turbine blades are used also become severe, a conventional 12Cr--Mo--V--N steel can not provide turbine blades having sufficient strength. Therefore, a stronger material is necessary. Accordingly the strength of material for long blades, tensile strength, which is a base of mechanical property, is required.
Further, toughness also is required to securing safety against rupture.
As a structural material having a higher tensile strength than the conventional 12Cr--Mo--V--N steel (martensite steel), a Ni-base alloy and Co-base alloy are well known. However, the are not sufficient in hot workability, machine-cutting property and vibration-attenuating properties, so that they are not desirable.
Material for gas turbine discs is disclosed in JP A 63-171856. Such material however, does not have a high tensile strength.
Further, an integral turbine, which has a high pressure side which and a low pressure side are integrated into one unit in view of space-saving in turbines of a small capacity less than 100,000 kW and a middle capacity of from 100,000 to 300,000 kW, has been put into practice. The length of final stage blades of this integral turbine is 33.5 inches at most because the strength of material for the rotor and blade is limited. The blade length, however, is desired to be further elongated in order to increase the turbine output.
JP A 3-130502 discloses blades for high and low pressure sides-integrated steam turbines, using 12% Cr steels. However, the steel is too low in tensile strength to provide long blades for recent low pressure steam turbines.